This invention relates to inductor apparatus and its application to ferroresonant regulators or constant voltage transformers. It is specifically concerned in one instance with a ferroresonant regulator with a shunt type tuned harmonic filter having plural inductors arranged on a unitary magnetic structure. In another instance, it is concerned with plural regulating inductors on a single magnetic structure for a multiphase controlled ferroresonant regulator.
The energy storage requirements of most inductor applications has generally dictated that each inductor winding be wound on a separate and independent magnetic core. In applications requiring a plurality of inductors, this requirement of a separate core for each inductor considerably increases the physical dimensions and overall weight of electrical equipment compared with those values if the same inductive effect could be achieved with fewer magnetic cores than inductors. One such instance is the output filter for a ferroresonant regulator.
The AC output voltage of a ferroresonant regulator normally includes a significant level of lower order harmonics. The third harmonic alone may have a magnitude as great as 25% of the output voltage. An AC output that is relatively free of harmonics is desirable, since it permits the ferroresonant regulator to operate more efficiently and be more stable in operation over a wider range of input voltage variation. Unless the output is applied to a harmonic reduction filter, the existence of these harmonics may damage load components which are energized directly by the AC output of the ferroresonant regulator.
It is common to use inductive type filters to reduce these harmonics in the AC output when an AC output signal is desired. One common harmonic reduction circuit uses an LC filter shunting the output, which is tuned to the third harmonic. This assures that the output is relatively free of third harmonics, but the fifth and seventh harmonic components can still represent a substantial portion of the output voltage.
In some applications requiring a very small harmonic content in the output, the output terminal is shunted by three separate harmonic filters tuned to the third, fifth and seventh harmonics, respectively. This, however, results in a bulky physical structure since three separate inductor cores are required. Use of a single unit, three leg core has proved impracticable because of magnetic coupling between the three windings.
Another arrangement disclosed in U.S. Pat. No. 2,694,177 issued to J. Sola, Nov. 9, 1954, avoids the need for a separate magnetic structure for the inductor by providing a separate magnetic path on the basic ferroresonant magnetic structure of the transformer. This arrangement, however, requires an extra set of shunts for the ferroresonant transformer core and complicates the design of the ferroresonant transformer. This becomes even less desirable when a particular transformer design must be capable of accommodating a wide range of output loads. Additionally, in some instances, the shunts may not be sufficient to achieve the desired inductance.